Flat panel registration fixture and method of using same

ABSTRACT

A registration fixture for use with a surgical navigation system for registration of medical images to a three-dimensional tracking space includes a base frame adapted to be mounted over a flat panel detector of an x-ray medical imaging device, and a side frame having optical tracking markers mounted to the base frame. The base frame includes a first set of radiopaque markers embedded therein in a first predetermined pattern and arranged on a plane, and a second set of radiopaque markers embedded therein in a second predetermined pattern also arranged on another plane, which is spaced from the first set of radiopaque markers. The side frame has a plurality of optical tracking markers and is configured to detachably mount to the base frame without piercing a sterilizing drape to be interposed between the base frame and the side frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 17/556,097, filed Dec. 20, 2021, which is incorporated hereinby reference in its entirety.

FIELD

The present disclosure relates to position recognition systems, and inparticular, the registration of a medical image to a three-dimensionaltracking space.

BACKGROUND

Orthopedic surgical navigation has the ability to improve patientoutcomes through decreased blood loss, radiation dose, and proceduraland anesthetic time in addition to increased accuracy and ease withwhich complex procedure can be performed. Two surgical navigationworkflows to achieving these outcome improvements are the fluoroscopyand pre-operative navigation workflows, which require a C-Arm imagingdevice and fluoroscopy registration fixture.

Conventionally, registration fixtures are mounted to an x-raytransmitter side. In some cases, however, it is an inaccurate way toregister the navigation system and may be inconvenient to attach thefixture due to the particular transmitter housing shape. Thus, it isdesirable to provide a system and method for an improved registrationfixture.

SUMMARY

According to one aspect of the present invention, a registration fixturefor use with a surgical navigation system for registration of medicalimages to a three-dimensional tracking space is provided. Theregistration fixture includes a base frame adapted to be mounted over aflat panel detector of an x-ray medical imaging device, and a side framehaving optical tracking markers which is mounted to the base frame. Thebase frame includes a first set of radiopaque markers embedded thereinin a first predetermined pattern and a second set of radiopaque markersembedded therein in a second predetermined pattern which is verticallyspaced from the first set of radiopaque markers. The side frame has aplurality of optical tracking markers and is configured to detachablymount to the base frame without piercing a sterilizing drape to beinterposed between the base frame and the side frame.

These and other systems, methods, objects, features, and advantages ofthe present invention will be apparent to those skilled in the art fromthe following detailed description of the preferred embodiment and thedrawings. All documents mentioned herein are hereby incorporated intheir entirety by reference.

BRIEF DESCRIPTION OF THE FIGURES

The invention and the following detailed description of certainembodiments thereof may be understood by reference to the followingfigures:

FIG. 1 is an overhead view of a potential arrangement for locations ofthe robotic system, patient, surgeon, and other medical personnel duringa surgical procedure;

FIG. 2 illustrates the robotic system including positioning of thesurgical robot and the camera relative to the patient according to oneembodiment;

FIG. 3 illustrates a surgical robotic system in accordance with anexemplary embodiment;

FIG. 4 illustrates a portion of a surgical robot in accordance with anexemplary embodiment;

FIG. 5 illustrates a block diagram of a surgical robot in accordancewith an exemplary embodiment;

FIG. 6 illustrates a surgical robot in accordance with an exemplaryembodiment;

FIGS. 7A-7C illustrate an end-effector in accordance with an exemplaryembodiment;

FIG. 8 illustrates a surgical instrument and the end-effector, beforeand after, inserting the surgical instrument into the guide tube of theend-effector according to one embodiment;

FIGS. 9A-9C illustrate portions of an end-effector and robot arm inaccordance with an exemplary embodiment;

FIG. 10 illustrates a dynamic reference array, an imaging array, andother components in accordance with an exemplary embodiment;

FIG. 11 illustrates a method of registration in accordance with anexemplary embodiment;

FIG. 12A-12B illustrate embodiments of imaging devices according toexemplary embodiments;

FIG. 13 shows one embodiment of a navigation fixture.

FIG. 14 illustrates an x-ray (fluoroscope) collector plate showing thetheoretical projection of small metallic spheres (hereafter referred toas ‘BBs’) within two planes at different distances from the source.

FIG. 15 illustrates two x-ray projections taken from the sameradio-opaque point from two different perspectives to produce a 3Dlocation.

FIG. 16 illustrates an x-ray image taken through a plane parallel to thecollector plate of a grid of BBs.

FIG. 17 illustrates key dimensions looking at a plane perpendicular tothe collector plate's plane, and with BBs in the field of view whoseshadows appear on the collector plate.

FIG. 18 illustrates a bb pattern on the two parallel plates and thedesign of the fixture, which mounts to the image intensifier of afluoroscopy unit.

FIG. 19 illustrates a BB pattern for a registration fixture.

FIG. 20 illustrates a fluoro registration fixture constructed fromparallel rings with crosshairs.

FIG. 21 illustrates an appearance of a ring registration fixture on anx-ray when the x-ray collector is parallel with the planes of the ringsand the rings are concentric with the x-ray collector.

FIG. 22 illustrates a theoretical appearance of a ring registrationfixture on an x-ray when the fixture is at a severe angle relative tothe collector plate and the rings.

FIG. 23 illustrates a transformation step for rotation by θ about z in acoordinate system mapping process.

FIG. 24 illustrates a transformation step for rotation about y by α in acoordinate system mapping process.

FIG. 25 illustrates a transformation step for rotation in plane to matcha radiograph's perspective in a coordinate system mapping process.

FIG. 26 illustrates a transformation step for displacement from acoordinate system center by dx, dy in a coordinate system mappingprocess.

FIG. 27 illustrates a transformation step of magnification according toparallax in a coordinate system mapping process.

FIG. 28 illustrates a schematic of key dimensions looking at a planeperpendicular to a collector plate's plane with rings parallel to thecollector in the field of view whose shadows appear on the collectorplate.

FIG. 29 illustrates a view across a ring that is at an arbitraryincidence angle to the collector plane from a perspective looking acrossthe ring plane, where the ring plane is in and out of the page.

FIG. 30 illustrates a view across a pair of concentric rings that are atan arbitrary incidence angle to the collector plane from a perspectivelooking across a ring plane, where the ring plane is in and out of thepage.

FIG. 31 illustrates a view of a ring at an arbitrary incidence anglefrom a rotated perspective.

FIG. 32 illustrates a view of a pair of rings at an arbitrary incidenceangle.

FIG. 33 illustrates a modeled appearance on an x-ray (with parallax) oftwo circular rings with an incidence angle of α=20° occurring about they-axis.

FIG. 34 illustrates a modeled appearance on an x-ray (with parallax) oftwo parallel circular rings with an incidence angle of α=24.5° occurringabout the y-axis, where both rings are offset from the center of thex-ray, and the long axis of both ellipses appears to be angled visiblyrelative to the y-axis

FIG. 35 illustrates a modeled appearance on an x-ray (with parallax) oftwo parallel circular rings with an incidence angle of α=24.5° occurringabout the y-axis, where both rings are offset from the center of thex-ray, and the far field ellipse has been scaled about the center of theimage until the near and far field ellipse are equal in their long axis.

FIG. 36 illustrates a pincushion distortion.

FIG. 37 illustrates an s-distortion.

FIG. 38 is a perspective view of a novel registration fixture which isdesigned to be attached to a flat panel detector of a medical imagingdevice according to one aspect of the invention.

FIG. 39 is a plan view of a radiolucent plate having two sets ofembedded radiopaque markers that are vertically spaced according to oneaspect of the invention.

FIG. 40A is a plan view of a first plate of the radiolucent plate ofFIG. 39 with a predetermined pattern of the radiopaque markers.

FIG. 40B is a plan view of a second plate of the radiolucent plate ofFIG. 39 with a predetermined pattern of the radiopaque markers.

FIG. 41 is a perspective view of a base frame and a side frame of theregistration fixture of FIG. 38 prior to assembly.

FIG. 42 is a side view of a kinematic mount of the side frame of FIG. 41illustrating a non-piercing clamp.

FIG. 43A is an outer perspective view of an alternative non-piercingkinematic clamp of the registration fixture of FIG. 38 .

FIG. 43B is an outer perspective view of an alternative non-piercingkinematic clamp of the registration fixture of FIG. 38 .

FIG. 44 is a cross-sectional view of the side frame of FIG. 43A.

FIG. 45 is a perspective view of the base frame of FIG. 38 with a set ofstraps and a ratchet for attachment to the flat panel detector.

FIG. 46 illustrates the base frame of FIG. 38 as attached to the flatpanel detector with the straps and ratchet as shown in FIG. 45 .

While the invention has been described in connection with certainpreferred embodiments, other embodiments would be understood by one ofordinary skill in the art and are encompassed herein.

DETAILED DESCRIPTION

It is to be understood that the present disclosure is not limited in itsapplication to the details of construction and the arrangement ofcomponents set forth in the description herein or illustrated in thedrawings. The teachings of the present disclosure may be used andpracticed in other embodiments and practiced or carried out in variousways. Also, it is to be understood that the phraseology and terminologyused herein is for the purpose of description and should not be regardedas limiting. The use of “including,” “comprising,” or “having” andvariations thereof herein is meant to encompass the items listedthereafter and equivalents thereof as well as additional items. Unlessspecified or limited otherwise, the terms “mounted,” “connected,”“supported,” and “coupled” and variations thereof are used broadly andencompass both direct and indirect mountings, connections, supports, andcouplings. Further, “connected” and “coupled” are not restricted tophysical or mechanical connections or couplings.

The following discussion is presented to enable a person skilled in theart to make and use embodiments of the present disclosure. Variousmodifications to the illustrated embodiments will be readily apparent tothose skilled in the art, and the principles herein can be applied toother embodiments and applications without departing from embodiments ofthe present disclosure. Thus, the embodiments are not intended to belimited to embodiments shown, but are to be accorded the widest scopeconsistent with the principles and features disclosed herein. Thefollowing detailed description is to be read with reference to thefigures, in which like elements in different figures have like referencenumerals. The figures, which are not necessarily to scale, depictselected embodiments and are not intended to limit the scope of theembodiments. Skilled artisans will recognize the examples providedherein have many useful alternatives and fall within the scope of theembodiments.

Turning now to the drawing, FIGS. 1 and 2 illustrate a surgical robotsystem 100 in accordance with an exemplary embodiment. Surgical robotsystem 100 may include, for example, a surgical robot 102, one or morerobot arms 104, a base 106, a display 110, an end-effector 112, forexample, including a guide tube 114, and one or more tracking markers118. The surgical robot system 100 may include a patient tracking device116 also including one or more tracking markers 118, which is adapted tobe secured directly to the patient 210 (e.g., to the bone of the patient210). The surgical robot system 100 may also utilize a camera 200, forexample, positioned on a camera stand 202. The camera stand 202 can haveany suitable configuration to move, orient, and support the camera 200in a desired position. The camera 200 may include any suitable camera orcameras, such as one or more infrared cameras (e.g., bifocal orstereophotogrammetric cameras), able to identify, for example, activeand passive tracking markers 118 in a given measurement volume viewablefrom the perspective of the camera 200. The camera 200 may scan thegiven measurement volume and detect the light that comes from themarkers 118 in order to identify and determine the position of themarkers 118 in three-dimensions. For example, active markers 118 mayinclude infrared-emitting markers that are activated by an electricalsignal (e.g., infrared light emitting diodes (LEDs)), and passivemarkers 118 may include retro-reflective markers that reflect infraredlight (e.g., they reflect incoming IR radiation into the direction ofthe incoming light), for example, emitted by illuminators on the camera200 or other suitable device.

FIGS. 1 and 2 illustrate a potential configuration for the placement ofthe surgical robot system 100 in an operating room environment. Forexample, the robot 102 may be positioned near or next to patient 210.Although depicted near the head of the patient 210, it will beappreciated that the robot 102 can be positioned at any suitablelocation near the patient 210 depending on the area of the patient 210undergoing the operation. The camera 200 may be separated from the robotsystem 100 and positioned at the foot of patient 210. This locationallows the camera 200 to have a direct visual line of sight to thesurgical field 208. Again, it is contemplated that the camera 200 may belocated at any suitable position having line of sight to the surgicalfield 208. In the configuration shown, the surgeon 120 may be positionedacross from the robot 102, but is still able to manipulate theend-effector 112 and the display 110. A surgical assistant 126 may bepositioned across from the surgeon 120 again with access to both theend-effector 112 and the display 110. If desired, the locations of thesurgeon 120 and the assistant 126 may be reversed. The traditional areasfor the anesthesiologist 122 and the nurse or scrub tech 124 remainunimpeded by the locations of the robot 102 and camera 200.

With respect to the other components of the robot 102, the display 110can be attached to the surgical robot 102 and in other exemplaryembodiments, display 110 can be detached from surgical robot 102, eitherwithin a surgical room with the surgical robot 102, or in a remotelocation. End-effector 112 may be coupled to the robot arm 104 andcontrolled by at least one motor. In exemplary embodiments, end-effector112 can comprise a guide tube 114, which is able to receive and orient asurgical instrument 608 (described further herein) used to performsurgery on the patient 210. As used herein, the term “end-effector” isused interchangeably with the terms “end-effectuator” and “effectuatorelement.” Although generally shown with a guide tube 114, it will beappreciated that the end-effector 112 may be replaced with any suitableinstrumentation suitable for use in surgery. In some embodiments,end-effector 112 can comprise any known structure for effecting themovement of the surgical instrument 608 in a desired manner.

The surgical robot 102 is able to control the translation andorientation of the end-effector 112. The robot 102 is able to moveend-effector 112 along x-, y-, and z-axes, for example. The end-effector112 can be configured for selective rotation about one or more of thex-, y-, and z-axis, and a Z Frame axis (such that one or more of theEuler Angles (e.g., roll, pitch, and/or yaw) associated withend-effector 112 can be selectively controlled). In some exemplaryembodiments, selective control of the translation and orientation ofend-effector 112 can permit performance of medical procedures withsignificantly improved accuracy compared to conventional robots thatutilize, for example, a six degree of freedom robot arm comprising onlyrotational axes. For example, the surgical robot system 100 may be usedto operate on patient 210, and robot arm 104 can be positioned above thebody of patient 210, with end-effector 112 selectively angled relativeto the z-axis toward the body of patient 210.

In some exemplary embodiments, the position of the surgical instrument608 can be dynamically updated so that surgical robot 102 can be awareof the location of the surgical instrument 608 at all times during theprocedure. Consequently, in some exemplary embodiments, surgical robot102 can move the surgical instrument 608 to the desired position quicklywithout any further assistance from a physician (unless the physician sodesires). In some further embodiments, surgical robot 102 can beconfigured to correct the path of the surgical instrument 608 if thesurgical instrument 608 strays from the selected, preplanned trajectory.In some exemplary embodiments, surgical robot 102 can be configured topermit stoppage, modification, and/or manual control of the movement ofend-effector 112 and/or the surgical instrument 608. Thus, in use, inexemplary embodiments, a physician or other user can operate the system100, and has the option to stop, modify, or manually control theautonomous movement of end-effector 112 and/or the surgical instrument608. Further details of surgical robot system 100 including the controland movement of a surgical instrument 608 by surgical robot 102 can befound in co-pending U.S. patent application Ser. No. 13/924,505, whichis incorporated herein by reference in its entirety.

The robotic surgical system 100 can comprise one or more trackingmarkers 118 configured to track the movement of robot arm 104,end-effector 112, patient 210, and/or the surgical instrument 608 inthree dimensions. In exemplary embodiments, a plurality of trackingmarkers 118 can be mounted (or otherwise secured) thereon to an outersurface of the robot 102, such as, for example and without limitation,on base 106 of robot 102, on robot arm 104, or on the end-effector 112.In exemplary embodiments, at least one tracking marker 118 of theplurality of tracking markers 118 can be mounted or otherwise secured tothe end-effector 112. One or more tracking markers 118 can further bemounted (or otherwise secured) to the patient 210. In exemplaryembodiments, the plurality of tracking markers 118 can be positioned onthe patient 210 spaced apart from the surgical field 208 to reduce thelikelihood of being obscured by the surgeon, surgical tools, or otherparts of the robot 102. Further, one or more tracking markers 118 can befurther mounted (or otherwise secured) to the surgical tools 608 (e.g.,a screw driver, dilator, implant inserter, or the like). Thus, thetracking markers 118 enable each of the marked objects (e.g., theend-effector 112, the patient 210, and the surgical tools 608) to betracked by the robot 102. In exemplary embodiments, system 100 can usetracking information collected from each of the marked objects tocalculate the orientation and location, for example, of the end-effector112, the surgical instrument 608 (e.g., positioned in the tube 114 ofthe end-effector 112), and the relative position of the patient 210.

In exemplary embodiments, one or more of markers 118 may be opticalmarkers. In some embodiments, the positioning of one or more trackingmarkers 118 on end-effector 112 can maximize the accuracy of thepositional measurements by serving to check or verify the position ofend-effector 112. Further details of surgical robot system 100 includingthe control, movement and tracking of surgical robot 102 and of asurgical instrument 608 can be found in co-pending U.S. patentapplication Ser. No. 13/924,505, which is incorporated herein byreference in its entirety.

Exemplary embodiments include one or more markers 118 coupled to thesurgical instrument 608. In exemplary embodiments, these markers 118,for example, coupled to the patient 210 and surgical instruments 608, aswell as markers 118 coupled to the end-effector 112 of the robot 102 cancomprise conventional infrared light-emitting diodes (LEDs) or anOptotrak® diode capable of being tracked using a commercially availableinfrared optical tracking system such as Optotrak®. Optotrak® is aregistered trademark of Northern Digital Inc., Waterloo, Ontario,Canada. In other embodiments, markers 118 can comprise conventionalreflective spheres capable of being tracked using a commerciallyavailable optical tracking system such as Polaris Spectra. PolarisSpectra is also a registered trademark of Northern Digital, Inc. In anexemplary embodiment, the markers 118 coupled to the end-effector 112are active markers which comprise infrared light-emitting diodes whichmay be turned on and off, and the markers 118 coupled to the patient 210and the surgical instruments 608 comprise passive reflective spheres.

In exemplary embodiments, light emitted from and/or reflected by markers118 can be detected by camera 200 and can be used to monitor thelocation and movement of the marked objects. In alternative embodiments,markers 118 can comprise a radio-frequency and/or electromagneticreflector or transceiver and the camera 200 can include or be replacedby a radio-frequency and/or electromagnetic transceiver.

Similar to surgical robot system 100, FIG. 3 illustrates a surgicalrobot system 300 and camera stand 302, in a docked configuration,consistent with an exemplary embodiment of the present disclosure.Surgical robot system 300 may comprise a robot 301 including a display304, upper arm 306, lower arm 308, end-effector 310, vertical column312, casters 314, cabinet 316, tablet drawer 318, connector panel 320,control panel 322, and ring of information 324. Camera stand 302 maycomprise camera 326. These components are described in greater withrespect to FIG. 5 . FIG. 3 illustrates the surgical robot system 300 ina docked configuration where the camera stand 302 is nested with therobot 301, for example, when not in use. It will be appreciated by thoseskilled in the art that the camera 326 and robot 301 may be separatedfrom one another and positioned at any appropriate location during thesurgical procedure, for example, as shown in FIGS. 1 and 2 . FIG. 4illustrates a base 400 consistent with an exemplary embodiment of thepresent disclosure. Base 400 may be a portion of surgical robot system300 and comprise cabinet 316. Cabinet 316 may house certain componentsof surgical robot system 300 including but not limited to a battery 402,a power distribution module 404, a platform interface board module 406,a computer 408, a handle 412, and a tablet drawer 414. The connectionsand relationship between these components is described in greater detailwith respect to FIG. 5 .

FIG. 5 illustrates a block diagram of certain components of an exemplaryembodiment of surgical robot system 300. Surgical robot system 300 maycomprise platform subsystem 502, computer subsystem 504, motion controlsubsystem 506, and tracking subsystem 532. Platform subsystem 502 mayfurther comprise battery 402, power distribution module 404, platforminterface board module 406, and tablet charging station 534. Computersubsystem 504 may further comprise computer 408, display 304, andspeaker 536. Motion control subsystem 506 may further comprise drivercircuit 508, motors 510, 512, 514, 516, 518, stabilizers 520, 522, 524,526, end-effector 310, and controller 538. Tracking subsystem 532 mayfurther comprise position sensor 540 and camera converter 542. System300 may also comprise a foot pedal 544 and tablet 546.

Input power is supplied to system 300 via a power source 548 which maybe provided to power distribution module 404. Power distribution module404 receives input power and is configured to generate different powersupply voltages that are provided to other modules, components, andsubsystems of system 300. Power distribution module 404 may beconfigured to provide different voltage supplies to platform interfacemodule 406, which may be provided to other components such as computer408, display 304, speaker 536, driver 508 to, for example, power motors512, 514, 516, 518 and end-effector 310, motor 510, ring 324, cameraconverter 542, and other components for system 300 for example, fans forcooling the electrical components within cabinet 316.

Power distribution module 404 may also provide power to other componentssuch as tablet charging station 534 that may be located within tabletdrawer 318. Tablet charging station 534 may be in wireless or wiredcommunication with tablet 546 for charging table 546. Tablet 546 may beused by a surgeon consistent with the present disclosure and describedherein. [0055] Power distribution module 404 may also be connected tobattery 402, which serves as temporary power source in the event thatpower distribution module 404 does not receive power from input power548. At other times, power distribution module 404 may serve to chargebattery 402 if necessary.

Other components of platform subsystem 502 may also include connectorpanel 320, control panel 322, and ring 324. Connector panel 320 mayserve to connect different devices and components to system 300 and/orassociated components and modules. Connector panel 320 may contain oneor more ports that receive lines or connections from differentcomponents. For example, connector panel 320 may have a ground terminalport that may ground system 300 to other equipment, a port to connectfoot pedal 544 to system 300, a port to connect to tracking subsystem532, which may comprise position sensor 540, camera converter 542, andcameras 326 associated with camera stand 302. Connector panel 320 mayalso include other ports to allow USB, Ethernet, HDMI communications toother components, such as computer 408. [0057] Control panel 322 mayprovide various buttons or indicators that control operation of system300 and/or provide information regarding system 300. For example,control panel 322 may include buttons to power on or off system 300,lift or lower vertical column 312, and lift or lower stabilizers 520-526that may be designed to engage casters 314 to lock system 300 fromphysically moving. Other buttons may stop system 300 in the event of anemergency, which may remove all motor power and apply mechanical brakesto stop all motion from occurring. Control panel 322 may also haveindicators notifying the user of certain system conditions such as aline power indicator or status of charge for battery 402.

Ring 324 may be a visual indicator to notify the user of system 300 ofdifferent modes that system 300 is operating under and certain warningsto the user.

Computer subsystem 504 includes computer 408, display 304, and speaker536. Computer 504 includes an operating system and software to operatesystem 300. Computer 504 may receive and process information from othercomponents (for example, tracking subsystem 532, platform subsystem 502,and/or motion control subsystem 506) in order to display information tothe user. Further, computer subsystem 504 may also include speaker 536to provide audio to the user.

Tracking subsystem 532 may include position sensor 504 and converter542. Tracking subsystem 532 may correspond to camera stand 302 includingcamera 326 as described with respect to FIG. 3 . Position sensor 504 maybe camera 326. Tracking subsystem may track the location of certainmarkers that are located on the different components of system 300and/or instruments used by a user during a surgical procedure. Thistracking may be conducted in a manner consistent with the presentdisclosure including the use of infrared technology that tracks thelocation of active or passive elements, such as LEDs or reflectivemarkers, respectively. The location, orientation, and position ofstructures having these types of markers may be provided to computer 408which may be shown to a user on display 304. For example, a surgicalinstrument 608 having these types of markers and tracked in this manner(which may be referred to as a navigational space) may be shown to auser in relation to a three dimensional image of a patient's anatomicalstructure. Motion control subsystem 506 may be configured to physicallymove vertical column 312, upper arm 306, lower arm 308, or rotateend-effector 310. The physical movement may be conducted through the useof one or more motors 510-518. For example, motor 510 may be configuredto vertically lift or lower vertical column 312. Motor 512 may beconfigured to laterally move upper arm 308 around a point of engagementwith vertical column 312 as shown in FIG. 3 . Motor 514 may beconfigured to laterally move lower arm 308 around a point of engagementwith upper arm 308 as shown in FIG. 3 . Motors 516 and 518 may beconfigured to move end-effector 310 in a manner such that one maycontrol the roll and one may control the tilt, thereby providingmultiple angles that end-effector 310 may be moved. These movements maybe achieved by controller 538 which may control these movements throughload cells disposed on end-effector 310 and activated by a user engagingthese load cells to move system 300 in a desired manner.

Moreover, system 300 may provide for automatic movement of verticalcolumn 312, upper arm 306, and lower arm 308 through a user indicatingon display 304 (which may be a touchscreen input device) the location ofa surgical instrument or component on three dimensional image of thepatient's anatomy on display 304. The user may initiate this automaticmovement by stepping on foot pedal 544 or some other input means.

FIG. 6 illustrates a surgical robot system 600 consistent with anexemplary embodiment. Surgical robot system 600 may compriseend-effector 602, robot arm 604, guide tube 606, instrument 608, androbot base 610. Instrument tool 608 may be attached to a tracking array612 including one or more tracking markers (such as markers 118) andhave an associated trajectory 614. Trajectory 614 may represent a pathof movement that instrument tool 608 is configured to travel once it ispositioned through or secured in guide tube 606, for example, a path ofinsertion of instrument tool 608 into a patient. In an exemplaryoperation, robot base 610 may be configured to be in electroniccommunication with robot arm 604 and end-effector 602 so that surgicalrobot system 600 may assist a user (for example, a surgeon) in operatingon the patient 210. Surgical robot system 600 may be consistent withpreviously described surgical robot system 100 and 300.

A tracking array 612 may be mounted on instrument 608 to monitor thelocation and orientation of instrument tool 608. The tracking array 612may be attached to an instrument 608 and may comprise tracking markers804. As best seen in FIG. 8 , tracking markers 804 may be, for example,light emitting diodes and/or other types of reflective markers (e.g.,markers 118 as described elsewhere herein). The tracking devices may beone or more line of sight devices associated with the surgical robotsystem. As an example, the tracking devices may be one or more cameras200, 326 associated with the surgical robot system 100, 300 and may alsotrack tracking array 612 for a defined domain or relative orientationsof the instrument 608 in relation to the robot arm 604, the robot base610, end-effector 602, and/or the patient 210. The tracking devices maybe consistent with those structures described in connection with camerastand 302 and tracking subsystem 532.

FIGS. 7A, 7B, and 7C illustrate a top view, front view, and side view,respectively, of end-effector 602 consistent with an exemplaryembodiment. End-effector 602 may comprise one or more tracking markers702. Tracking markers 702 may be light emitting diodes or other types ofactive and passive markers, such as tracking markers 118 that have beenpreviously described. In an exemplary embodiment, the tracking markers702 are active infrared-emitting markers that are activated by anelectrical signal (e.g., infrared light emitting diodes (LEDs)). Thus,tracking markers 702 may be activated such that the infrared markers 702are visible to the camera 200, 326 or may be deactivated such that theinfrared markers 702 are not visible to the camera 200, 326. Thus, whenthe markers 702 are active, the end-effector 602 may be controlled bythe system 100, 300, 600, and when the markers 702 are deactivated, theend-effector 602 may be locked in position and unable to be moved by thesystem 100, 300, 600. Markers 702 may be disposed on or withinend-effector 602 in a manner such that the markers 702 are visible byone or more cameras 200, 326 or other tracking devices associated withthe surgical robot system 100, 300, 600. The camera 200, 326 or othertracking devices may track end-effector 602 as it moves to differentpositions and viewing angles by following the movement of trackingmarkers 702. The location of markers 702 and/or end-effector 602 may beshown on a display 110, 304 associated with the surgical robot system100, 300, 600, for example, display 110 as shown in FIG. 2 and/ordisplay 304 shown in FIG. 3 . This display 110, 304 may allow a user toensure that end-effector 602 is in a desirable position in relation torobot arm 604, robot base 610, the patient 210, and/or the user.

For example, as shown in FIG. 7A, markers 702 may be placed around thesurface of end-effector 602 so that a tracking device placed away fromthe surgical field 208 and facing toward the robot 102, 301 and thecamera 200, 326 is able to view at least 3 of the markers 702 through arange of common orientations of the end-effector 602 relative to thetracking device 100, 300, 600. For example, distribution of markers 702in this way allows end-effector 602 to be monitored by the trackingdevices when end-effector 602 is translated and rotated in the surgicalfield 208.

In addition, in exemplary embodiments, end-effector 602 may be equippedwith infrared (IR) receivers that can detect when an external camera200, 326 is getting ready to read markers 702. Upon this detection,end-effector 602 may then illuminate markers 702. The detection by theIR receivers that the external camera 200, 326 is ready to read markers702 may signal the need to synchronize a duty cycle of markers 702,which may be light emitting diodes, to an external camera 200, 326. Thismay also allow for lower power consumption by the robotic system as awhole, whereby markers 702 would only be illuminated at the appropriatetime instead of being illuminated continuously. Further, in exemplaryembodiments, markers 702 may be powered off to prevent interference withother navigation tools, such as different types of surgical instruments608.

FIG. 8 depicts one type of surgical instrument 608 including a trackingarray 612 and tracking markers 804. Tracking markers 804 may be of anytype described herein including but not limited to light emitting diodesor reflective spheres. Markers 804 are monitored by tracking devicesassociated with the surgical robot system 100, 300, 600 and may be oneor more of the line of sight cameras 200, 326. The cameras 200, 326 maytrack the location of instrument 608 based on the position andorientation of tracking array 612 and markers 804. A user, such as asurgeon 120, may orient instrument 608 in a manner so that trackingarray 612 and markers 804 are sufficiently recognized by the trackingdevice or camera 200, 326 to display instrument 608 and markers 804 on,for example, display 110 of the exemplary surgical robot system.

The manner in which a surgeon 120 may place instrument 608 into guidetube 606 of the end-effector 602 and adjust the instrument 608 isevident in FIG. 8 . The hollow tube or guide tube 114, 606 of theend-effector 112, 310, 602 is sized and configured to receive at least aportion of the surgical instrument 608. The guide tube 114, 606 isconfigured to be oriented by the robot arm 104 such that insertion andtrajectory for the surgical instrument 608 is able to reach a desiredanatomical target within or upon the body of the patient 210. Thesurgical instrument 608 may include at least a portion of a generallycylindrical instrument. Although a screw driver is exemplified as thesurgical tool 608, it will be appreciated that any suitable surgicaltool 608 may be positioned by the end-effector 602. By way of example,the surgical instrument 608 may include one or more of a guide wire,cannula, a retractor, a drill, a reamer, a screw driver, an insertiontool, a removal tool, or the like. Although the hollow tube 114, 606 isgenerally shown as having a cylindrical configuration, it will beappreciated by those of skill in the art that the guide tube 114, 606may have any suitable shape, size and configuration desired toaccommodate the surgical instrument 608 and access the surgical site.

FIGS. 9A-9C illustrate end-effector 602 and a portion of robot arm 604consistent with an exemplary embodiment. End-effector 602 may furthercomprise body 1202 and clamp 1204. Clamp 1204 may comprise handle 1206,balls 1208, spring 1210, and lip 1212. Robot arm 604 may furthercomprise depressions 1214, mounting plate 1216, lip 1218, and magnets1220. [0072] End-effector 602 may mechanically interface and/or engagewith the surgical robot system and robot arm 604 through one or morecouplings. For example, end-effector 602 may engage with robot arm 604through a locating coupling and/or a reinforcing coupling. Through thesecouplings, end-effector 602 may fasten with robot arm 604 outside aflexible and sterile barrier. In an exemplary embodiment, the locatingcoupling may be a magnetically kinematic mount and the reinforcingcoupling may be a five bar over center clamping linkage.

With respect to the locating coupling, robot arm 604 may comprisemounting plate 1216, which may be non-magnetic material, one or moredepressions 1214, lip 1218, and magnets 1220. Magnet 1220 is mountedbelow each of depressions 1214. Portions of clamp 1204 may comprisemagnetic material and be attracted by one or more magnets 1220. Throughthe magnetic attraction of clamp 1204 and robot arm 604, balls 1208become seated into respective depressions 1214. For example, balls 1208as shown in FIG. 9B would be seated in depressions 1214 as shown in FIG.9A. This seating may be considered a magnetically-assisted kinematiccoupling. Magnets 1220 may be configured to be strong enough to supportthe entire weight of end-effector 602 regardless of the orientation ofend-effector 602. The locating coupling may be any style of kinematicmount that uniquely restrains six degrees of freedom.

With respect to the reinforcing coupling, portions of clamp 1204 may beconfigured to be a fixed ground link and as such clamp 1204 may serve asa five bar linkage. Closing clamp handle 1206 may fasten end-effector602 to robot arm 604 as lip 1212 and lip 1218 engage clamp 1204 in amanner to secure end-effector 602 and robot arm 604. When clamp handle1206 is closed, spring 1210 may be stretched or stressed while clamp1204 is in a locked position. The locked position may be a position thatprovides for linkage past center. Because of a closed position that ispast center, the linkage will not open absent a force applied to clamphandle 1206 to release clamp 1204. Thus, in a locked positionend-effector 602 may be robustly secured to robot arm 604.

Spring 1210 may be a curved beam in tension. Spring 1210 may becomprised of a material that exhibits high stiffness and high yieldstrain such as virgin PEEK (poly-ether-ether-ketone). The linkagebetween end-effector 602 and robot arm 604 may provide for a sterilebarrier between end-effector 602 and robot arm 604 without impedingfastening of the two couplings.

The reinforcing coupling may be a linkage with multiple spring members.The reinforcing coupling may latch with a cam or friction basedmechanism. The reinforcing coupling may also be a sufficiently powerfulelectromagnet that will support fastening end-effector 102 to robot arm604. The reinforcing coupling may be a multi-piece collar completelyseparate from either end-effector 602 and/or robot arm 604 that slipsover an interface between end-effector 602 and robot arm 604 andtightens with a screw mechanism, an over center linkage, or a cammechanism.

Referring to FIGS. 10 and 11 , prior to or during a surgical procedure,certain registration procedures may be conducted in order to trackobjects and a target anatomical structure of the patient 210 both in anavigation space and an image space. In order to conduct suchregistration, a registration system 1400 may be used as illustrated inFIG. 10 .

In order to track the position of the patient 210, a patient trackingdevice 116 may include a patient fixation instrument 1402 to be securedto a rigid anatomical structure of the patient 210 and a dynamicreference base (DRB) 1404 may be securely attached to the patientfixation instrument 1402. For example, patient fixation instrument 1402may be inserted into opening 1406 of dynamic reference base 1404.Dynamic reference base 1404 may contain markers 1408 that are visible totracking devices, such as tracking subsystem 532. These markers 1408 maybe optical markers or reflective spheres, such as tracking markers 118,as previously discussed herein.

Patient fixation instrument 1402 is attached to a rigid anatomy of thepatient 210 and may remain attached throughout the surgical procedure.In an exemplary embodiment, patient fixation instrument 1402 is attachedto a rigid area of the patient 210, for example, a bone that is locatedaway from the targeted anatomical structure subject to the surgicalprocedure. In order to track the targeted anatomical structure, dynamicreference base 1404 is associated with the targeted anatomical structurethrough the use of a registration fixture that is temporarily placed onor near the targeted anatomical structure in order to register thedynamic reference base 1404 with the location of the targeted anatomicalstructure.

A registration fixture 1410 is attached to patient fixation instrument1402 through the use of a pivot arm 1412. Pivot arm 1412 is attached topatient fixation instrument 1402 by inserting patient fixationinstrument 1402 through an opening 1414 of registration fixture 1410.Pivot arm 1412 is attached to registration fixture 1410 by, for example,inserting a knob 1416 through an opening 1418 of pivot arm 1412.

Using pivot arm 1412, registration fixture 1410 may be placed over thetargeted anatomical structure and its location may be determined in animage space and navigation space using tracking markers 1420 and/orfiducials 1422 on registration fixture 1410. Registration fixture 1410may contain a collection of markers 1420 that are visible in anavigational space (for example, markers 1420 may be detectable bytracking subsystem 532). Tracking markers 1420 may be optical markersvisible in infrared light as previously described herein. Registrationfixture 1410 may also contain a collection of fiducials 1422, forexample, such as bearing balls, that are visible in an imaging space(for example, a three dimension CT image). As described in greaterdetail with respect to FIG. 11 , using registration fixture 1410, thetargeted anatomical structure may be associated with dynamic referencebase 1404 thereby allowing depictions of objects in the navigationalspace to be overlaid on images of the anatomical structure. Dynamicreference base 1404, located at a position away from the targetedanatomical structure, may become a reference point thereby allowingremoval of registration fixture 1410 and/or pivot arm 1412 from thesurgical area.

FIG. 11 provides an exemplary method 1500 for registration consistentwith the present disclosure. Method 1500 begins at step 1502 wherein agraphical representation (or image(s)) of the targeted anatomicalstructure may be imported into system 100, 300 600, for example computer408. The graphical representation may be three dimensional CT or afluoroscope scan of the targeted anatomical structure of the patient 210which includes registration fixture 1410 and a detectable imagingpattern of fiducials 1420.

At step 1504, an imaging pattern of fiducials 1420 is detected andregistered in the imaging space and stored in computer 408. Optionally,at this time at step 1506, a graphical representation of theregistration fixture 1410 may be overlaid on the images of the targetedanatomical structure.

At step 1508, a navigational pattern of registration fixture 1410 isdetected and registered by recognizing markers 1420. Markers 1420 may beoptical markers that are recognized in the navigation space throughinfrared light by tracking subsystem 532 via position sensor 540. Thus,the location, orientation, and other information of the targetedanatomical structure is registered in the navigation space. Therefore,registration fixture 1410 may be recognized in both the image spacethrough the use of fiducials 1422 and the navigation space through theuse of markers 1420. At step 1510, the registration of registrationfixture 1410 in the image space is transferred to the navigation space.This transferal is done, for example, by using the relative position ofthe imaging pattern of fiducials 1422 compared to the position of thenavigation pattern of markers 1420.

At step 1512, registration of the navigation space of registrationfixture 1410 (having been registered with the image space) is furthertransferred to the navigation space of dynamic registration array 1404attached to patient fixture instrument 1402. Thus, registration fixture1410 may be removed and dynamic reference base 1404 may be used to trackthe targeted anatomical structure in both the navigation and image spacebecause the navigation space is associated with the image space.

At steps 1514 and 1516, the navigation space may be overlaid on theimage space and objects with markers visible in the navigation space(for example, surgical instruments 608 with optical markers 804). Theobjects may be tracked through graphical representations of the surgicalinstrument 608 on the images of the targeted anatomical structure.

FIGS. 12A-12B illustrate imaging devices 1304 that may be used inconjunction with robot systems 100, 300, 600 to acquire pre-operative,intra-operative, post-operative, and/or real-time image data of patient210. Any appropriate subject matter may be imaged for any appropriateprocedure using the imaging system 1304. The imaging system 1304 may beany imaging device such as imaging device 1306 and/or a C-arm 1308device. It may be desirable to take x-rays of patient 210 from a numberof different positions, without the need for frequent manualrepositioning of patient 210 which may be required in an x-ray system.As illustrated in FIG. 12A, the imaging system 1304 may be in the formof a C-arm 1308 that includes an elongated C-shaped member terminatingin opposing distal ends 1312 of the “C” shape. C-shaped member 1130 mayfurther comprise an x-ray source 1314 and an image receptor 1316. Thespace within C-arm 1308 of the arm may provide room for the physician toattend to the patient substantially free of interference from x-raysupport structure 1318. As illustrated in FIG. 12B, the imaging systemmay include imaging device 1306 having a gantry housing 1324 attached toa support structure imaging device support structure 1328, such as awheeled mobile cart 1330 with wheels 1332, which may enclose an imagecapturing portion, not illustrated. The image capturing portion mayinclude an x-ray source and/or emission portion and an x-ray receivingand/or image receiving portion, which may be disposed about one hundredand eighty degrees from each other and mounted on a rotor (notillustrated) relative to a track of the image capturing portion. Theimage capturing portion may be operable to rotate three hundred andsixty degrees during image acquisition. The image capturing portion mayrotate around a central point and/or axis, allowing image data ofpatient 210 to be acquired from multiple directions or in multipleplanes. Although certain imaging systems 1304 are exemplified herein, itwill be appreciated that any suitable imaging system may be selected byone of ordinary skill in the art.

There are methods for displaying the simulated projection of a surgicaltool overlaid on a fluoroscopic image to assist in surgery throughone-way registration of the medical image to the tracking space. Forexample, a calibrating fixture may be attached to the image intensifierof a fluoroscope, such as illustrated in FIG. 13 . The fixture containsrows of small metallic spheres (hereafter referred to as ‘BBs’) withknown spacing that appear on the x-ray image, and also contains anoptical tracking array that provides the three-dimensional (3D) positionof the fixture in the tracking space. Through image processing andgeometric computations, it can be determined how a tool placed in thepath of the x-rays should appear as a projection on the x-ray image. The3D position of the tool, which has a tracking array attached, is trackedin the coordinate system of the tracker (e.g., cameras). Then, agraphical representation of the tool is overlaid on the x-ray images toprovide “virtual fluoroscopy” with roughly the same visual informationthat would be seen if continuous x-rays were taken while holding thetool in the surgical field. A benefit of this method is that the patientand medical staff are exposed to much less radiation as the virtualfluoroscopy can provide continuous updates of tool position overlaid ona single x-ray image.

Although this method maps 3D tool position to two-dimensional (2D)medical images, it is not necessary for that application to map pointsdetected on the 2D medical images to the 3D tracking space, i.e., toco-register the medical image space with the tracking space. However, itis possible to obtain such mapping by considering the vectors extendingfrom emitter to collector. FIG. 14 illustrates an x-ray (e.g.,fluoroscope) collector plate 1702 showing the theoretical projection ofBBs 1710 within two planes 1704 and 1706 at different distances from thesource 1708. X-ray collector plate 1702, Plane 1 1706, and Plane 2 1704are shown as being parallel and concentric. In this instance, the x-rayemitter 1708 is assumed to be a point, and rays from the source tocollector travel out from this point in a conical pattern. Because ofthis conical pattern, the BBs 1710 from Plane 1 1706 appear magnified onthe x-ray collector plate 1702 relative to the BBs 1710 from Plane 21704, although they are actually spaced the same in this example. Thisphenomenon is known as parallax.

Considering a case where one x-ray view is taken from a perspectivesubstantially different than another x-ray view, such as depicted inFIG. 15 , and where the exact positions of the collector and emitter in3D are known from tracking or other means, the vectors extending in aconical pattern from emitter to collector can be traced back to wherethey intersect an anatomical point of interest 1802 that is present inboth views. In this instance, “vectors” could mean vectors determinedfrom visible x-ray shadows of the BBs, or any vector calculated (e.g.,interpolated) to match the conical pattern deduced from the visiblex-ray shadows. The 3D position of that anatomical point of interest maythen be determined because there is a unique solution at theintersection of the vectors from the two views. That is, from one view,it is not possible to deduce 3D position of a reference point becausethe point could be anywhere along the vector from source to emitter andwould appear at the same location on the collector plate. The secondview provides the unique position along the vector where the point mustbe.

FIG. 14 shows just 4 BBs 1710 on two parallel planes 1704 and 1706.These BBs could provide the basis for methods to detect the position ofan object in 3D from multiple 2D x-ray views. However, to provide betteraccuracy, a dense grid of BBs such as shown in FIG. 16 (e.g., tens orhundreds) could be used instead, which would allow vectors to be moreaccurately interpolated. The use of more BBs allows more accurateinterpolation and ultimately better 3D accuracy, but x-ray shadows frommore BBs also obstructs the surgeon from being able to visualize theanatomy of interest on the x-ray image.

Implicit assumptions are that the positions of the collector plate andemitter source are known in 3D during both shots. For instance, thecollector plate may have a tracking array attached and its 3D positionwould therefore be directly tracked. It may also be possible to place atracker on the emitter. However, there are disadvantages to doing so,mainly that the tracking field needs to be very large to observe bothtrackers, where the distance between collector and emitter may typicallybe on the order of one meter. Tracking systems such as optical trackersmay only have a tracking field less than one cubic meter. Additionally,the emitter could be positioned out of view for some clinically typicalx-ray shots. The emitter source location could instead be calibratedrelative to the collector array, but the extrapolated accuracy indefining the emitter location may be low with a large distance betweencollector and emitter and the different amounts of sag when thefluoroscope is oriented differently. Alternatively, the emitter sourcedistance and direction relative to the collector may be calculated fromfluoroscopic images of two parallel planes of BBs with known spacingd_(ab) 1712, such as is shown in FIG. 14 and FIG. 17 . The equationsprovided in Equation 1 hold based on the geometry 2000 depicted in FIG.17 .

$\begin{matrix}{\frac{kL_{2a}}{d_{ec}} = \frac{l_{a}}{z_{ea}}} & {{Equation}1}\end{matrix}$$\frac{kL_{2b}}{d_{ec}} = {\frac{l_{b}}{z_{eb}} = \frac{l_{b}}{( {z_{ea} + d_{ab}} )}}$

where,

-   -   d_(ec) is the distance from emitter to collector in mm;    -   k is the scaling factor to convert pixel coordinates on the        fluoro output to mm;    -   l_(a) is the distance laterally in mm within Plane A between        BB1a and BB2a;    -   l_(b) is the distance laterally in mm within Plane B between        BB1b and BB2b;    -   y_(1a) is the distance in mm from the central beam laterally to        BB1a;    -   y_(1b) is the distance in mm from the central beam laterally to        BB1b;    -   y_(2a) is the distance in mm from the central beam laterally to        BB2a;    -   y_(2b) is the distance in mm from the central beam laterally to        BB2b;    -   z_(ea) is the distance in mm from the emitter to Plane A (BB1a        and BB2a);    -   z_(eb) is the distance in mm from the emitter to Plane B (BB1b        and BB2b);    -   d_(ab) is the distance in mm longitudinally between Plane A and        Plane B;    -   L_(2a) is the distance in pixel coordinates between the shadows        of the BBs in Plane A on the collector; and    -   L_(2b) is the distance in pixel coordinates between the shadows        of the BBs in Plane    -   B on the collector.

Solving for d_(ec) produces

$\begin{matrix}{\frac{d_{ec}}{k} = \frac{d_{ab}L_{2a}L_{2b}}{{l_{b}L_{2a}} - {l_{a}L_{2b}}}} & {{Equation}2}\end{matrix}$

Therefore, if the spacing between the planes is known and the spacingbetween the BBs is known, the distance from the emitter to collector canbe determined through image processing of an x-ray image containingthese BBs. Note that FIG. 17 indicates that the distances betweenshadows of two adjacent BBs in two planes are measured. In practice, thedistances between several pairs of BBs on the x-ray image may bemeasured and these distances averaged. Additionally, FIG. 17 shows thedistances between BBs on Plane A and Plane B as being the same, however,their physical distances may differ and is accounted for by l_(a) andl_(b) in the equations. In practice, it may be desirable to make the BBsoffset rather than spaced the same and aligned to prevent theirprojections from partially obscuring each other.

This method for defining the position of the emitter relative to thecollector makes use of the two parallel plates in defining the directionof the emitter as well as the distance. With the registration fixturemounted to the collector, the direction from emitter to collector isassumed to be perpendicular to the plane of the collector and the planescontaining BBs. If this assumption is untrue, the projections of BBsfrom the near and far field planes will not be symmetrically overlaid onx-ray images. For a given amount of angular deviation of the x-ray planefrom the BB planes, the amount of offset of BB shadows from asymmetrical projection is proportional to the distance between BBplanes, with larger plane separation manifesting as larger lateraldisplacements of the projections on the x-ray images. Through geometry,the lateral offsets of BB shadows can be used to determine accuratelythe actual orientation of the BB planes relative to the collector planeand therefore the position of the emitter in 3D, or used to manually orautomatically adjust the orientation of the registration fixture on theimage intensifier until BB planes and collector plate are trulycoplanar.

The scaling factor k is present in the above equation, but this factoris necessary for subsequent 3D to 2D mapping of the 3D coordinates of ageneralized point. In general, to map a 3D point with coordinates x, y,z onto a 2D x-ray image that has the X and Y axes of the image alignedwith the x and y axes of the Cartesian coordinate system, Equation 3holds.

$\begin{matrix}{X = {x( \frac{d_{ec}}{kz} )}} & {{Equation}3}\end{matrix}$ $Y = {y( \frac{d_{ec}}{kz} )}$

Where X is the coordinate axis of the 2D x-ray image aligned with theCartesian X-axis, Y is the coordinate axis of the 2D x-ray image alignedwith the Cartesian y-axis, and z is the Cartesian axis perpendicular tothe x-ray image.

If two fluoroscope shots are taken at different orientations up to 90degrees apart, such as one common clinical anteroposterior shot and onecommon clinical lateral shot, then (X1, Y1) could be defined as thex-ray coordinates of a point (x, y, z) as the point appears on an x-rayimage 1 (e.g., an anteroposterior image). The Cartesian coordinates ofthe point in a local coordinate system aligned with that x-ray planecould be defined as (x1, y1, z1). Similarly, (X2, Y2) could be definedas the x-ray coordinates of the same point as it appears on an x-rayimage 2 (e.g., a lateral image). The Cartesian coordinates of the pointin a local coordinate system aligned with that x-ray plane could bedefined as (x2, y2, z2). Because a tracking system may be used to detectthe 3D position of the x-ray collector while the fluoroscope is in eachorientation, the transformation T12 from Cartesian coordinate system 1to Cartesian coordinate system 2 is known, with T12 being a standard 4×4transformation matrix as is commonly used in the field. There istherefore a unique solution that results in Equation 4.

$\begin{matrix}{X_{1} = {x_{1}( \frac{d_{ec}}{kz_{1}} )}} & {{Equation}4}\end{matrix}$ $Y_{1} = {y_{1}( \frac{d_{ec}}{kz_{1}} )}$$X_{2} = {x_{2}( \frac{d_{ec}}{kz_{2}} )}$$Y_{2} = {y_{2}( \frac{d_{ec}}{kz_{2}} )}$ and$\begin{bmatrix}x_{2} \\y_{2} \\z_{2}\end{bmatrix} = {T_{12}\begin{bmatrix}x_{1} \\y_{1} \\z_{1}\end{bmatrix}}$

Note that the two coordinate systems are each oriented with their z-axisperpendicular to each x-ray plane, the origin of their z-axis at eachx-ray plane, and the origins of their x and y axes at the center of thex-ray plane. The direction of x and y relative to the x-ray planes maybe arbitrary. By tracking the locations of the x-ray planes in 3D, usingfor example 3D optical tracking, the transformation from the first tothe second 3D coordinate system (T12) can be determined.

A method for defining the 3D Cartesian coordinate system associated withtwo fluoroscopic views may assume that the BBs are projected uniformlyonto the image intensifier. However, distortion is commonly associatedwith images obtained from fluoroscopes, such as pincushion distortion,s-distortion, and the like. These types of distortion may be correctedusing image processing before applying the methods described herein.Distortion correction may make use of the fact that the BBs are arrangedin a symmetrical pattern on the registration device. Therefore, thex-rays projected through the known symmetrical pattern should create animage with matching symmetry. Spacing between BBs and alignment of rowsof BBs may be determined through image processing and compared to theexpected projections of the BBs. Algorithms commonly known in imageprocessing such as affine transformations and the like may be used toforce the projected x-ray image to match the known and expectedsymmetry. Since the same correction may also be applied to anatomicalimages on the x-rays, the resulting x-ray images should representundistorted projections and should allow valid calculation ofregistration as described herein.

In embodiments, the symmetrical pattern used for correcting distortioncould be a square pattern as depicted in FIG. 16 , a radiallysymmetrical pattern in which BBs are distributed in a polar coordinatesystem about the center of the image, where BBs share common radii andazimuth angles, or any suitable pattern as depicted in the fixture inFIGS. 18 and 19 . As long as the pattern of actual BBs embedded in theregistration fixture is known, the corresponding shadows of the BBs onx-ray images can be predicted and distortion correction applied to forcethe image to match the expected pattern.

The process of 2D to 3D mapping of images relies on the correctinterpretation of direction on the x-ray image. For example, if a 2Dx-ray image is an anteroposterior image, it must be known if the 2Dimage represents a shot with emitter anterior and collector posterior ora shot with emitter posterior and collector anterior. Additionally,since fluoroscopic images are commonly round, there must be a way toprecisely determine from the BB shadows which direction points left,right, up or down. The fixture's plane of BB's may provide informationfor alignment correction, such as using BB's located closest to thex-ray collector to provide information to orient the x-ray imagerotationally and also with regard to reflection, e.g., the BB patternmay determine whether the positive z direction extends off the front orback of the visible plane. In embodiments, the fixture may contain anouter ring of large BBs that are arranged so it uniquely identifiesaspects of alignment, such as the rotation and flip of the image. Thepattern of BBs for identifying orientation and/or flip may be chosenbased on the ability of the pattern to provide a unique combination ofimage rotation and flip and on the ability of pattern to provideredundant BBs for increased reliability of detection. Redundant BBs maybe important because it is possible that not all BBs would be visible onany given x-ray shot due to obstruction of the BB shadow from tools orimplants, or poor x-ray penetration through parts of the image.

In embodiments, a ring of BBs of varying spacing around the perimeter ofa standard circular fluoroscopic image may be employed, such asillustrated in FIG. 19 where the shadows of the perimeter BBs form a bitcode (e.g., 32 bit code). In embodiments, a first plane 2202 with afirst array of points and a second plane 2204 with a second array ofpoints may be projected to form a combined image 2206. Code lengthsshould be selected to enable the spacing of the BBs to be far enoughapart so there is a small chance that an error in detecting a BB'slocation could result in it falsely falling into an adjacent bitlocation while still providing enough information to be robust tomissing bits. If only a subset of the existing BBs is detected, with afew of the BB shadows not detectable, comparison of the subset against aknown template may provide the correct image orientation and flipregardless of which BBs are missing. If a subset with a greater numberof BBs missing is detected, an algorithm may determine the correct imageorientation and flip. In embodiments, knowing the limitations of thealgorithm, the system may require that a certain minimum number of BBsis detected before allowing the algorithm to proceed.

In embodiments, orientation matching may utilize a point match algorithm(e.g., the Kabsch point match algorithm) or other suitable point matchalgorithm that assumes both point sets are scaled the same. Thealgorithm may then determine the transformation between two point sets,where one point set comes from the orientation BB detection and theother point set comes from a fixture 3D model. The fixture's orientationmarkers may then be projected into image space. Since both point setsneed to be scaled the same, the algorithm tests a range of projectionscaling to find the best match. Once the best match is found thetransform is scaled appropriately, and the algorithm assigns pointcorrespondence between the detected image markers and the physicalfixture markers. The resulting transform can then be applied to theimage to rotate and/or flip it to produce alignment with the fixture.

Ring Registration Fixture:

As an alternative to an array of BBs to establish orientation, it ispossible to use rings or other shapes, such as formed from radio-opaquematerials such as metal wire, as fiducials in a registration fixture.Referring to FIG. 20 , a ring registration fixture 2300 is illustratedwith two parallel rings 2304 and 2306 of the same or different diameters(e.g., between 50-300 mm), are positioned concentrically in parallelplanes spaced apart (e.g., spaced apart by 50-300 mm). To facilitateidentification of the centers of the rings 2304 and 2306, the rings mayalso have one or more crosshairs 2308A and 2308B formed of wire or otherradio-opaque material of the same or different diameter as the ringsthemselves. Some desirable features of the rings include rings that areexactly circular, that their crosshairs pass through the exact center sothat diameters of the projected ellipses and crosshair intersectionpoints are accurate, and the like. Additionally, it may be desirablethat the cross-section of a ring be circular instead of flattened, sothat if the ring is at an angle relative to the x-ray image it isproperly projected. Possible methods for fashioning rings includewelding or otherwise adhering segments of wire, rapid prototyping (3Dprinting) using a radiopaque building material, etching in the samemanner as is used for fabrication of printed circuit boards, and thelike.

When an x-ray image is taken of the ring registration fixture 2300 whilecentered on a collector plate, it should appear as two concentriccircles 2402 and 2404, such as shown on FIG. 21 . If the x-ray image istaken while the ring registration fixture 2300 is not parallel to thecollector plate or centered, it would appear as two ellipses 2502 and2504 such as illustrated in FIG. 22 .

In addition, tracking markers 2302A-D may be used as references for ringpositioning of the ring registration fixture 2300 in 3D, such asutilizing an array of optical markers, a magnetic sensor, or other like3D tracking method. For reference it may be convenient to define a localcoordinate system on the registration fixture 2300. For example, areference local coordinate system may have its origin at the center ofthe ring that is closer to the x-ray emitter, with the second (e.g.,parallel) ring closer to the collector, and the x-axis and y-axis may becoincident with the crosshairs that identify the first ring's center,where the z-axis is coincident with the vector joining the centers ofthe two rings.

In embodiments, mapping points from 3D to 2D using a ring registrationfixture may utilize vectors through known points on both rings that arecreated to form a conical pattern, where this pattern is then used tointerpolate vectors through regions of interest.

In embodiments, a sequence of common transformations may be applied(i.e., rotations, translations, magnification), such as with thetransformation parameters estimated from features on the images. As anexample, consider a 3D coordinate system based on a two-ring fixturesuch that the coordinate system is centered on a first ring nearer tothe emitter as a near field ring and a second ring that is nearer to thecollector as a far field ring. In this example, near and far field ringsmay be the same diameter, where in order to map a point from thiscoordinate system to the coordinate system of the collector plate, anumber of transformations may be applied.

A non-limiting example set of illustrative transformations are depictedin FIGS. 23-27 . FIG. 23 depicts a transformation step 1 rotating by θabout z (e.g., θ is the angle allowing subsequent rotation α to occurabout y). Note that in this figure, the rings are viewed in 3D withoutparallax, and so the near and far field rings exactly overlap in thestarting orientation. FIG. 24 depicts a transformation step 2 rotatingabout y by α. Note that rotation occurs about the center of the nearfield ring (e.g., the ring closer to the emitter). FIG. 25 depicts atransformation step 3 rotating in plane to match the radiograph'sperspective (e.g., finding the angle in the x-y plane off of y to get tothe actual axis of rotation instead of using y axis as the axis ofrotation for incidence angle α). FIG. 26 depicts a transformation step 4displacing from coordinate system center by dx, dy. FIG. 27 depicts atransformation step 5 magnifying according to parallax. In this example,with step 5 complete, the x-y plane represents the points mapped to the2D plane. In step 5 magnification occurs according to Equation 3.

In this example, on the final image the near field ring appears moremagnified than the far field ring since points on the near field ringhave larger z values than the points on the far field ring.Additionally, rotation of the rings in x-y plane may appear differentdepending on how far the rings are from x, y=0, 0.

Thus, to go from a point in 3D that is specified in a coordinate systemattached to the ring registration fixture to a point in 2D on the x-rayplane, a sequence of transformations is applied where there are fiveunknowns: θ, α, ϕ, dx, and dy. It is possible to use image processing toestimate these five unknowns from the rings themselves. Therefore, oncethese five parameters are defined and registration is established, anynew point specified as x, y, z in the reference coordinate system may bedirectly mapped to the x-ray image coordinates.

For many of the calculations for determining the five parameters fromthe images, the ratio of d_(ec)/k is needed, as was described respect tothe BB fixture. This ratio may be determined similarly from an x-rayimage taken of the rings while oriented parallel to the collector plate.FIG. 28 illustrates a schematic of key dimensions looking at a planeperpendicular to the collector plate's plane, and with rings parallel tothe collector in the field of view whose shadows appear on the collectorplate. Based on FIG. 28 , the following equations can be written todetermine d_(ec)/k:

$\begin{matrix}{\frac{d_{ec}}{k} = \frac{d_{ab}L_{2a}L_{2b}}{{l_{b}L_{2a}} - {l_{a}L_{2b}}}} & {{Equation}5}\end{matrix}$

Where

-   -   d_(ec) is the distance from emitter to collector in mm;    -   k is the scaling factor to convert pixel coordinates on the        fluoro output to mm;    -   l_(a) is the diameter of Ring A;    -   l_(b) is the diameter of Ring B;    -   y_(1a) is the distance in mm from the central beam laterally to        the edge of Ring A;    -   y_(1b) is the distance in mm from the central beam laterally to        the edge of Ring B;    -   y_(2a) is the distance in mm from the central beam laterally to        opposite edge of Ring A;    -   y_(2b) is the distance in mm from the central beam laterally to        opposite edge of Ring B;    -   z_(ea) is the distance in mm from the emitter to Plane A (to        Ring A);    -   z_(eb) is the distance in mm from the emitter to Plane B (to        Ring B);    -   d_(ab) is the distance in mm longitudinally between Plane A and        Plane B;    -   L_(2a) is the diameter in pixel coordinates of the shadow of        Ring A on the collector; and    -   L_(2b) is the diameter in pixel coordinates of the shadow of        Ring B on the collector.

Non-limiting examples of how the five unknowns (0, a, dx, and dy) may bedetermined will now be described.

Calculating Angle of Incidence α:

Consider a conical beam hitting a plane of arbitrary angle relative tothe cone and projecting the image on to the collection plate, as viewedfrom the perspective depicted in FIG. 29 , where the view across a ringis at an arbitrary incidence angle to the collector plane from aperspective looking across the ring plane. The ring plane is in and outof the page as shown in the inset, where the view is from positive z andthe reformatted x and y axes are directed as shown in the 3D coordinatesystem. In this example, the distance from the top of the cone (e.g.,the x-ray emitter) to the collector on which the image is perceived,d_(ec), is fixed. Subscript ‘a’ is used because there is a second ringparallel to this one with the same incidence angle α and diameterl_(0b), this second ring having subscript ‘b’. Note that the coordinatesystems of the plate and the 3D space above it are positioned such thatthe center of the 2D image is at X_(p)=0 and the center of the 3D spaceis also at x_(r)=0.

Based on FIG. 29 , the following equations hold:

$\begin{matrix}{\frac{kX_{p1a}}{d_{ec}} = \frac{x_{r1a}}{z_{r1a}}} & {{Equation}6}\end{matrix}$ $\frac{kX_{p2a}}{d_{ec}} = \frac{x_{r2a}}{z_{r2a}}$

Referring to FIG. 30 , now consider a fixture with two parallel rings ofdifferent diameters. The parameters z_(ea) and z_(eb) represent thedistance in z direction from the emitter to the midpoint (intersectionof crosshairs) of each ring. FIG. 30 illustrates a view across a pair ofconcentric rings that are at an arbitrary incidence angle to thecollector plane from a perspective looking across the ring plane, wherethe ring plane is in and out of the page (see inset). Based on FIG. 30 ,the following equation holds:

$\begin{matrix}{{\cos\alpha} = \frac{z_{eb} - z_{ea}}{d_{ab}}} & {{Equation}7}\end{matrix}$

To solve for z_(ea) (and z_(eb)) consider the other perspective of thering, as viewed across the widest part as illustrated in FIG. 31 , whichprovides a view of the ring at an arbitrary incidence angle from aperspective rotated 90 degrees from that of FIG. 29 and FIG. 30 . Fromthis follows:

For ring a

$\begin{matrix}{\frac{l_{0a}}{z_{ea}} = \frac{kL_{2a}}{d_{ec}}} & {{Equation}8}\end{matrix}$

For ring b

$\begin{matrix}{\frac{l_{0b}}{z_{eb}} = \frac{kL_{2b}}{d_{ec}}} & {{Equation}9}\end{matrix}$ Or $\begin{matrix}{z_{ea} = \frac{d_{ec}l_{0a}}{kL_{2a}}} & {{Equation}10}\end{matrix}$ $z_{eb} = \frac{d_{ec}l_{0b}}{kL_{2b}}$

Plugging into equation 7,

$\begin{matrix}{{z_{eb} - z_{ea}} = {d_{ab}\cos\alpha}} & {{Equation}11}\end{matrix}$${\frac{d_{ec}l_{0b}}{kL_{2b}} - \frac{d_{ec}l_{0a}}{kL_{2a}}} = {d_{ab}\cos\alpha}$$\frac{{d_{ec}l_{0b}L_{2a}} - {d_{ec}l_{0a}L_{2b}}}{kL_{2a}L_{2b}} = {d_{ab}\cos\alpha}$$\alpha = {\cos^{- 1}\lbrack \frac{d_{ec}( {{l_{0b}L_{2a}} - {l_{0a}L_{2b}}} )}{kd_{ab}L_{2a}L_{2b}} \rbrack}$

Where

-   -   L_(2a)=widest diameter of elliptical projection of ring a in        pixel coordinates;    -   L_(2b)=widest diameter of elliptical projection of ring b in        pixel coordinates;    -   d_(ec)=distance in mm from emitter to collector;    -   d_(ab)=shortest distance in mm from ring a to ring b;    -   k=conversion factor for pixels to mm;    -   l₀ _(a) =known actual diameter of ring a in mm; and    -   l₀ _(b) =known actual diameter of ring b in mm.

Equation 11 dictates that the widest and narrowest projections of therings be measured, and slight variations may lead to discrepancies in a.It is useful to seek an equation based on displacement of the ringcenters instead, which is less sensitive to error. If the lower ring is“magnified” to match the known ratio of diameters of upper and lowerrings (e.g., ratio of 1 if the rings are the same diameter), it would bethe same as if the ring were moved up in the vertical direction (zdirection) since scaling is done for values of each point on the ring inthe coordinate system where ring points are offset from zero. FIG. 32 .Illustrates a view of a pair of rings at an arbitrary incidence anglefrom the same perspective as FIG. 29 . If the far field ring ismagnified to match the magnification of the near field ring, it would beequivalent to physically moving the ring up the z-axis untilz_(ea)=z_(eb).

This z position becomes the z position of the major axis of bothellipses. Image processing enables the scaling of the image of the farfield ellipse about the center of the image until the far field ellipsediameter relative to the near field ellipse diameter match the expectedratio. For example, if the far field ring and near field ring physicallyhave identical diameters, the x-ray projected far field ellipse willappear smaller than the near field ellipse. Points on the far fieldellipse may then be scaled so that a new image of the far field ellipsewould have the same diameter as the near field ellipse. In particular,the only point that needs to be scaled may be the center of the farfield ellipse, as defined by the intersection of the far field ring'scrosshairs. With the far field ellipse scaled and the near field ellipsenot scaled, the offset in the centers of the ellipses represents themeasurement in image coordinates of the side opposite in a triangle withhypotenuse equal to the distance between rings. At this z position, thehypotenuse may be determined in image coordinates, where it is thedistance between rings times the ratio of near field ellipse major axisover the near field ring diameter (or times the ratio of the scaled farfield ellipse major axis over the far field ring diameter, which is bydefinition of the scaling factor the same). With the side opposite andhypotenuse, α can be found with an arcsine function.

$\begin{matrix}{\alpha = {\sin^{- 1}( \frac{D_{cab}}{L_{2a}( \frac{d_{ab}}{l_{0a}} )} )}} & {{Equation}12}\end{matrix}$

Where:

-   -   D_(cab)=distance in image coordinates between the center of the        un-scaled near field; ellipse and the scaled far field ellipse;    -   L_(2a)=diameter of near field ellipse in image coordinates        measured in the direction of the axis of rotation (roughly        equivalent to projected ellipse's major axis);    -   l₀ _(a) =diameter of near field ring in mm; and    -   d_(ab)=distance between rings in mm.        Calculating azimuth angle ϕ:

It might appear that the azimuth angle ϕ (the angle required to put theaxis of rotation for ring incidence on the y-axis) is just the anglerelative to the major axis of one of the ellipses. For example, FIG. 33depicts a modeled appearance on an x-ray (with parallax) of two circularrings with an incidence angle of α=20° occurring about the y-axis. Thelong axis of both ellipses appears to be oriented in line with they-axis and therefore an azimuth angle of ϕ=0° would be expected.Seemingly, the orientation of the long axis of either or both ellipsescan be assessed using image processing and used for determining θ.However, it can be seen that the long axes of the ellipses do notaccurately reflect the azimuth angle if the ring positions are offsetfrom the center of the image. In the example depicted in FIG. 34 , whichwas generated from numerical data, there is clear discrepancy in theorientations of the major axes of the two ellipses. In FIG. 34 a modeledappearance is depicted on an x-ray (with parallax) of two parallelcircular rings with an incidence angle of α=24.5° occurring about they-axis. Both rings are offset from the center of the x-ray. The longaxis of both ellipses appears to be angled visibly relative to they-axis; additionally, the long axis of the larger ellipse appears tohave a different azimuth angle than that of the smaller ellipse. In thiscase, the azimuth angle is known to be ϕ=0° but image processing wouldnot have correctly given this angle.

An additional consideration is that for small angles, it may bedifficult to accurately assess the exact direction in which the diameteris largest, thus a method for using the orientation of the major axis ofan ellipse to find θ may produce a lower accuracy result. Inembodiments, a method using the length of the major axis of an ellipseshould produce better results.

In the scaling exercise described in reference to FIG. 32 , it can beseen that magnification is equivalent to moving the entire ring up thez-axis. Therefore, if the far field ring is scaled appropriately, thetwo elliptical ring images will represent a projection at the same zcoordinate of the near and far field rings. If the center of the nearand far field rings are at the same z coordinate, then the vectorconnecting them in x and y represents the path of the axis of rotation.The actual axis of rotation should be perpendicular to this path andalso in the x-y plane. Therefore, the axis of rotation may be extractedthrough image processing by first scaling the far field ring center thentracing the path connecting the centers of the far field and near fieldring images. In an illustration, FIG. 35 depicts a modeled appearance onan x-ray (with parallax) of two parallel circular rings with anincidence angle of α=24.5° occurring about the y-axis. Both rings areoffset from the center of the x-ray. The far field ellipse has beenscaled about the center of the image until the near and far fieldellipses are equal in their long axis. The azimuth angle is known to beϕ=0° (i.e., rotation about the y axis—see FIG. 24 ) which is the correctresult after scaling has been performed.

The angle θ is the angle of the near field vertical crosshair relativeto Y or horizontal crosshair relative to X after accounting for theperspective. Thus, finding the locations of the intersections ofcrosshairs with the ellipses and then applying an inverse incidenceangle would give the intersection points in a flat plane, allowing theangle θ to be determined from an arctangent of the x, y coordinates ofthe crosshair intersection point.

Note that it is important to know which crosshair is aligned with X or Yand which direction of a crosshair points to +X or +Y. This informationcan be determined from additional features on the fixture that appear onx-ray images, such as a BB or wire near the reference crosshair'spositive axis or any other suitable feature.

The offset position dx, dy is the offset of the x,y coordinate of thecenter of the near field ring. This point can be directly tracked basedon the tracker on the fixture and the corresponding point seen on theresulting x-ray. This point can serve as a registration check. That is,if a navigated probe is pointed at the center of the near field ring, animage of a probe with its tip at the projected ellipse's crosshairintersection should be seen.

If the registration fixture is attached very precisely to the imageintensifier, then several of the parameters referenced above go to zero.That is, the incidence angle α, axis of rotation reference ϕ,displacements dx and dy all go to zero, simplifying the registrationprocess. Thus, as with the BB fixture, the locations of intersections ofcrosshairs and rings on x-rays could be used as adjustment tools insteadof for extracting transformation parameters. That is, if an x-ray showsdisparity in the intersections of the ring centers and edges, such asdepicted in FIG. 21 , the fixture could be adjusted manually orautomatically on the image intensifier until the x-rays show centering,at which point the transformations would be simplified and mapping wouldbe at its best accuracy.

When using rings in a registration fixture, correction of distortion maybe achieved in a way that is similar to the correction applied for a BBfixture. In order for distortion correction to be effective, thecrosshairs on the ring fixture require an additional feature in whichevenly spaced markings are placed along each crosshair. These markingscould be hatch marks, circles, gaps, or any such feature that appears ona visible projection on the x-ray image. Then, by considering both thelinearity of the crosshairs and the spacing between indices on thecrosshairs, pincushion and s-distortion may be accounted for andcorrected. The FIGS. 36 and 37 show manifestations of pincushion ands-distortion on images when using ring fixtures. It is assumed thatsince pincushion distortion is radially symmetrical about the center ofthe image, it is only necessary to see one crosshair and the markings toaccount for the pincushion distortion and correct it, assuming thecrosshair runs through the image center from one edge to the other. Ifpincushion distortion is not symmetrical at different angles, thenadditional crosshairs may be needed to assess the magnitude ofpincushion in different directions.

FIG. 36 illustrates a pincushion distortion that might occur with afluoroscope that would cause an x-ray that is shot through a square wiregrid to appear as a pincushion distorted image 3602. For clarity, thepincushion pattern is shown more exaggerated than would be typical. Inthe lower part of the figure, a ring with crosshairs and evenly spacedgaps in the crosshairs is shown undistorted 3604 (left) and then withpincushion distortion 3606 (right). Note that the distortion has noeffect on the ring but shows clearly on the spacing of the gaps in thecrosshairs, with increasing spacing visible from the center outward tothe ring. The magnitude of pincushion distortion is measured as theamount of increase in spacing between indices going from the center tothe edge of the image. Similarly, barrel distortion would manifest asdecreasing gaps in the crosshairs from image center to ring.

FIG. 37 illustrates an s-distortion that might occur with a fluoroscopethat would cause an x-ray that is shot through a square wire grid toappear as is shown as an s-distorted image 3702. For clarity, thes-pattern is shown more exaggerated than would be typical. In the lowerpart of the figure, a ring with crosshairs is shown undistorted 3704(left) and then with s-distortion 3706 (right). Note that the distortionhas no effect on the ring but shows clearly on the crosshairs, whichhave taken on the s-shape. The magnitude of s distortion is measuredfrom the amount by which the two crosshairs take on the s-shape.

3D Surgical Planning in 2D:

In the planning of medical procedures, such as in conjunction with asurgical robot platform, planning for placement of medical objects suchas surgical screws may be provided in 3D based on the 2D images. Forinstance, in such planning a line segment drawn to represent a screw inone of the 2D views may be assumed to have a certain dimension into andout of the plane in which it is drawn (e.g., in the z dimension). It canalso be assumed to have a certain starting and ending z coordinate intoand out of the plane in which it is drawn. For example, if a pediclescrew is being planned on an anteroposterior and lateral x-ray image, anappropriate assumption for the z coordinates could be that the dimensionof the screw on the lateral x-ray represents the maximum length of thescrew. That is, the screw is not angled into or out of the plane andtherefore the z coordinate of the tip and tail of the screw on thelateral image's local coordinate system are the same. The z coordinate,which is equal for tip and tail, could be assumed to be a value thatwould be appropriate to place the screw at the center of theanteroposterior image. That is, for the user selecting x- andy-coordinates in the lateral planar view, whatever z coordinate in thelateral image causes the screw image to appear at the center of thescreen on the anteroposterior image would be used.

In embodiments, other means could be used for improved initial guesseson the unknown planning plane. For example, anteroposterior and lateralimages could be used for planning, where the top of both images could beoriented to represent the rostral anatomical direction. If it is knownthrough software prompting that the user is about to place the leftscrew by dropping it on the lateral image, the starting location of thescrew on the anteroposterior image could be toward the left side of thescreen, assuming left screen is left anatomical direction.

Once an initial position is dictated by the user in one view and guessedor otherwise specified by software in the other view, any subsequentrepositioning of the screw in either view may be mapped to the otherview through satisfying the forward mapping of the 3D coordinates to 2D.For example, the user may have defined the x, y, z coordinates of ascrew's tip in a local Cartesian coordinate system associated with theregistration fixture during a lateral x-ray. If, through softwareinteractions, the user then selects and drags the representation of thescrew tip, they must be moving the tip in the x-y plane of thatCartesian coordinate system, not in its z direction, since the x-y planeof the Cartesian coordinate system is parallel to the image plane. The xand y movements (with z movement=0) in that local coordinate system canbe updated through the user interaction. Then, because thetransformation between the local coordinate systems of theanteroposterior and lateral x-rays are known through tracking, theresulting x, y, z coordinates associated with the anteroposteriorimage's local coordinate system can also be updated, allowing mapping ofthe planned tip of the screw on to a new position in the anteroposteriorimage. Through a sequence of updating one image and then the other, theuser can move the screw into a 3D position that is known relative toboth tracked positions of the registration fixture and therefore knownto the camera space and to the robot. The robot can then move to aposition to allow the screw to be placed accurately.

Note that if the two coordinate systems of the images are perpendicular,one representing the anteroposterior and one representing the lateralx-ray, then movement of a planned representation of a screw tip or tailon the anteroposterior view in the rostrocaudal direction throughsoftware interaction would have the effect of causing the screw tip ortail representation to move rostrocaudally in the lateral view by thesame amount. However, movement of the screw tip or tail left or right inthe anteroposterior view may have no effect on the planned tip or tailposition in the lateral image. Conversely, movement anterior orposterior of the screw tip or tail in the lateral image would have noeffect on the screw tip or tail position in the anteroposterior image,but movement of the screw tip or tail position rostrally or caudally inthe lateral image would cause the representation of the screw tip ortail in the anteroposterior image to change rostrocaudally by the sameamount. If the two x-rays are not taken perpendicular, then movementleft, right, up or down in one view of the planned screw tip or tailwill cause the representation in the other view to move by at least someamount.

Although it has been described that two views are used for planning,such as one anteroposterior and one lateral x-ray, since the mapping of3D to 2D can be created for any x-ray image it is possible tosimultaneously display and update a plan on any number of x-ray imagesas long as the registration fixture's tracking information is acquiredat the time the image is taken. For example, four images shot at45-degree increments could be displayed in four quadrants of the screenand a planned screw could be registered to each view. Using softwareinteractions to update the planned position in one view would cause theimage in each of the other views to change.

FIGS. 38-46 illustrate a novel registration fixture 2 which isconfigured for attachment to a flat panel detector 4 side of a medicalimaging device, rather than the transmitter side. The registrationfixture 2 of FIG. 38 is ideally suited for a medical imaging device thatuse a digital flat panel detector 4 on a C-Arm to take advantage ofdigital imaging technology, which include lower radiation dose andenhanced image quality as compared to an image intensifier based C-Armsystems.

The registration fixture 2 includes a base frame 6, first and secondside frames 8,10 and a kinematic mount 12 that detachably attaches tothe base frame 6. By definition, the kinematic mount restrains all sixdegrees of freedom of the side frames 8,10 relative to the base frame 6.

The base frame 6 is composed of an aluminum frame of minimized volumeand weight, but can be fabricated from any of a number of reasonablecost, low density, high strength and stiffness materials.

A radiolucent plate 14 is attached to the base frame 6. In theembodiment shown in FIG. 39 , the plate 16 includes two plates 14,16that are vertically spaced from each other. An orientation plate 14 ispositioned closer to the flat panel detector 4 and a registration plate16 is positioned above the orientation plate.

Each plate is manufactured from a radiolucent material (e.g., carbonfiber, Rohacell foam, acrylic, ABS, or similar material) and housesembedded radiopaque markers 17,19 oriented in unique configurations forimage processing and navigation purposes. In the embodiment shown, theradiopaque markers 17,19 are ⅛ inch stainless steel balls, but could becomposed of any number of radiopaque materials and of a variety ofgeometries.

In one embodiment, the plates 14, 16 are mounted to a precision flatsurface on the base frame 6 and a separation distance between the twoplates is between 10 mm and 75 mm. In another embodiment, the range isbetween 25 mm and 50 mm, which may minimize obstruction within asurgical work area for the clinical team. Nevertheless, the plateseparation distance can be increased or decreased to improve accuracy.

The orientation and registration plates 14, 16 are aligned withprecision dowel pins 20 through a hole and slot configuration to achieveoptimal plate to plate alignment precision. The hole, slot, pinconfiguration for the two plates are unique to prevent incorrectinstallation.

FIG. 40A shows the orientation plate 16 having a first set of radiopaquemarkers 17 in a predetermined pattern while FIG. 40B shows theregistration plate 18 having a second set of radiopaque markers 19 in apredetermined pattern.

The second set of markers 19 in the registration plate 18 includes aplurality of radiopaque markers that are equally spaced from each otherin a circular pattern. In the embodiment shown, there are 24 uniformlyspaced markers in the registration plate 18.

The first set of markers 17 in the orientation plate 16 includes a setof markers that are spaced from each other in a circular patternalthough the spacing among them is non-uniform. The circle formed by themarkers 17 is smaller in diameter than the one defined by the second setof markers 19 in the registration plate 18. The two circles defined bythe markers (smaller circle defined by markers 17 and larger circledefined by markers 19) are coaxial and concentric with one another.

The first set of markers 17 also includes markers (e.g., two shown foreach of the corresponding non-uniformly spaced markers) that extendradially outwardly from the corresponding marker in the small circledefined by the non-uniform markers such that an imaginary line from thecenter of the circle crosses the radially extending markers and thecorresponding marker in the circle. In the embodiment shown, there are24 markers 17 in the orientation plate 16 (8 markers lying on the smallcircle and 8 subsets of 2 radially extending markers from thecorresponding marker in the circle). It is important to note that thenumber of markers in both the registration plate 18 and the orientationplate 16 are the same at 24.

All radiopaque markers may be in the form of stainless steel balls orBBs' although they may be of any suitable radiopaque material.

The placement, size and the number of the radiopaque markers in theregistration and orientation plates as described above provide optimalparameters for navigation accuracy, collimation requirements (i.e.,ability to detect enough markers and place surgical implants accuratelyeven with the presence of collimation which will truncate the patterns),minimization of anatomical obstruction to the surgeon during navigatedprocedures, and detection of orientation to allow navigation trackingsoftware to deterministically detect whether the image is not flipped by180-degrees or 90-degrees.

Although the radiolucent plate 14 is described with reference to a flatpanel registration fixture 2, they may be implemented as part of aregistration fixture (such as shown in FIG. 18 ) which is configured tobe attached to a transmitter side of the imaging device.

The side frame has a plurality of optical tracking markers and isadapted to detachably mount to the base frame 6 without piercing asterilizing drape to be interposed between the base frame 6 and the sideframe.

As shown in FIG. 38 , each side frame includes six flat disk markers andsix spherical markers that are in fixed relationship with the radiopaquemarkers. The side frames 8,10 may be constructed from aluminum or anynumber of materials providing adequate strength, stiffness, weight, andoptical properties relative to system accuracy requirements.

The side frames 8,10 may be bead blasted and black anodized to reducepotential reflections, among many surface treatment options. In theembodiment shown, the two side frames 8,10 are oriented 180-degrees fromone another, and extend perpendicularly from the base frame 6. Each sideframe 8, 10 may contain mounting features to enable the use of both flattracking disks 22 and spherical markers 24 (only the posts are shown inFIG. 38 ) in order to allow both NIR and visible light tracking.

The flat disk markers 22 and spherical markers 24 are interspersed witheach other. In one embodiment, the pattern and spacing of the markers22,24 on one side frame 8 is identical to that of the other side frame10 when viewing from their respective side (i.e., 180 degrees from eachother).

The side frames 8,10 are self-aligning and oriented precisely to thebase frame 6 through the use of a kinematic mount configuration 12.

Each side frame 8, 10 is designed to be non-interchangeable through theincorporation of a physical keying feature, which prevents users fromaccidental incorrect installation.

As shown in FIGS. 38, 41 and 42 , the base frame 6 includes three spacedapart kinematic mount points 28 (recesses shown as three vee blocks)configured to mount to corresponding kinematic mounts points 26 (shownas three truncated spherical balls) on the base frame 6 byself-alignment.

As shown in FIG. 42 , a non-piercing clamp 30 includes a rotary pin 34and a camming handle 36 coupled to the rotary pin and configured to moveor translate the U-shaped clamp 32 so as to press the U-shaped clampagainst the base frame 6. The U-shaped clamp 32 has a slot 42 (see FIG.43A) that receives a part of the side frame 8 to allow a translationalor sliding movement relative to the side frame in order to compress orrelease the base frame 6. In an alternate embodiment as shown in FIG. 38, the U-shaped clamp 32 is mountable over a side wall of the base frame6 and a handle 38 having a threaded shaft 40 threadably coupled to theU-shaped clamp such that rotation of the handle presses the U-shapedclamp against the base frame 6 in order to fix the side frame 8 to thebase frame 6.

The first side frame 8 extends laterally on one side of the base frame 6and its tracking markers 22,24 face away from the base frame 6 in afirst direction away from the base frame while the second side frame 10extends laterally on the other side of the base frame 6 and its trackingmarkers 22,24 face away from the base frame 6 in a second directionopposite the first direction.

As shown in FIG. 38 , the first and second side frames 8,10 are parallelto each other when mounted to the base frame 6. In the embodiment shown,the two side frames 8,10 are mounted perpendicularly to the base frame6.

In one embodiment, the spherical tracking markers 24 of the side frames8,10 are adapted to reflect infrared light (NIR) while flat disk markers22 are adapted to reflect visible light and in some embodiments also theinfrared light (NIR).

In order to facilitate the ability to mount to a variety of flat panelC-Arm detector housings, multiple flexible ratchet strap configurationshave been designed and implemented.

FIG. 45 shows a ratchet strap assembly 46 including a set of straps48,50, a pad assembly 52 and a ratchet 54 for attachment to the flatpanel detector 4. FIG. 46 illustrates the base frame 6 of FIG. 38 asattached to the flat panel detector 4 with the ratchet strap assembly 46as shown in FIG. 45 . One end of a first strap 50 is rotationallyattached to the base frame 6 and the other end is attached to theratchet 54 through the pad assembly 52. One end of a second strap 48(ladder strap) is rotationally coupled to the base frame 6 and the otherside is coupled to the ratchet 54 for sliding adjustment relative to thefirst strap 50. The ratchets 54 allow adjustment of the straps 48,50 tofit over a variety of flat panel detectors 4. The ratchet strapassemblies 46 are available, for example, at M2 Inc. of Colchester, Vt.The straps 48,50 extend from the base frame 6 and is configured to wraparound an underside of the flat panel detector 4 to temporarily fix thebase frame 6 to the detector panel of the x-ray medical imaging deviceduring use.

In one configuration, the first strap 50 of the ratchet strap assemblyis composed of an extension component containing multiple thru holes tofacilitate adjustability (FIG. 45 ). In another configuration, one endof the first strap 50 is attached to a hook component such as a springloaded carabiner that attaches to a ring or a handle disposed behind theflat panel detector 4.

A flat panel detector registration fixture 2 as described above providesthe following advantages.

Image collimation is possible while still allowing adequate orientationand registration fiducial marker detection for navigation and imageprocessing requirements. Collimation has major advantages with respectto image quality as visualization of patient anatomy in certainscenarios can be extremely challenging without such collimation.

Optical tracking arrays mount to a precision kinematic mountconfiguration utilizing a clamp that prevents piercing of sterile drape.The clamp is designed in a u-shaped geometry which moves by either acamming handle integrated as actuator or a threaded handle (acting as aleadscrew) for rigid mounting to the base frame 6. Such mountingstrategy protects the integrity of the sterile drape.

Non-piercing side frames 8,10 with optical tracking markers facilitateclamping of a separable, sterile, and autoclavable side frame which isunlike the conventional design that uses drape-piercing mountmethodology. Side frames 8,10 containing optical tracking markers areseparable from the base frame 6, utilize disposable markers, and aremachine washable and autoclavable. The separable nature of the sideframes 8,10 allows increased optimization for improved accuracy: size,segment length optimization, positioning relative to potential operatingroom obstructions.

Optical tracking arrays incorporate both passively tracked disks andspheres into single frame assembly to facilitate tracking utilizing NIR(spherical markers) and visible light technology (flat disk markers).

Novel radiopaque fiducial pattern is incorporated into orientation andregistration plates to facilitate image processing and navigationworkflows.

Ratchet strap mounting configuration utilizing a non-deterministic,compliant strap to facilitate fluoroscopy fixture mounting to a varietyof c-arm detector panel geometries. Ratchet strap includes an adjustableextension component fastened in series to a compliant pad withspring-loaded mechanical ratchet, which interfaces with flexible ladderstrap belt assembly. Ladder strap may optionally contain a hook orcarabiner component for mounting to captive C-Arm handles. Optionaldesign safety elements incorporated on belt assembly include hard stops.

Modular ratchet strap assembly has the ability to be adjusted along theperimeter of fluoroscopy fixture through utilization of self lockingclevis pin, incorporating spring loaded wedge or equivalent locating andself-locking feature. Clevis pin incorporation facilitates easy useradjustment of ratchet strap assembly considering a variety of C-Armdetector housings.

Orientation and registration plate spacing has been minimized to between25 mm to 50 mm in one embodiment to minimize obstruction within surgicalwork volume for clinical team, as compared to conventional fluorofixtures with 100 mm or greater plate separation distance. This plateseparation may be decreased or increased to improve accuracy, but hasbeen minimized in order to maximize available workspace for clinicalsurgical team.

While the invention has been disclosed in connection with the preferredembodiments shown and described in detail, various modifications andimprovements thereon will become readily apparent to those skilled inthe art. Accordingly, the spirit and scope of the present invention isnot to be limited by the foregoing examples, but is to be understood inthe broadest sense allowable by law.

All documents referenced herein are hereby incorporated by reference.

What is claimed is:
 1. A registration fixture for use with a surgicalnavigation system for registration of medical images to athree-dimensional tracking space comprising: a base frame adapted to bemounted to an x-ray medical imaging device; a plate attached to the baseframe, the plate having a first set of radiopaque markers embeddedtherein in a first predetermined pattern and a second set of radiopaquemarkers embedded therein in a second predetermined pattern; the firstset of markers including a plurality of non-uniformly arranged markerslying on a first circle; the second set of markers including a pluralityof uniformly arranged markers lying on a second circle different thanthe first circle.
 2. The registration fixture of claim 1, wherein: thefirst set of markers are arranged in a first plane; the second set ofmarkers are arranged in a second plane offset from the first plane. 3.The registration fixture of claim 3, wherein the first circle is smallerin diameter than the second circle.
 4. The registration fixture of claim1, wherein the first set of markers include a plurality of subsets ofmarkers with each subset of markers and a corresponding marker in thefirst circle lying on an imaginary line from the center of the firstcircle.
 5. The registration fixture of claim 4, wherein each subset ofmarkers includes at least two markers that are positioned outside of thesecond circle.
 6. The registration fixture of claim 5, wherein thenumber of markers of the first set and the second set is the same. 7.The registration fixture of claim 6, wherein the number of markers ofthe first set and the second set is each
 24. 8. The registration fixtureof claim 1, wherein the plate includes: an orientation plate having thefirst set of markers embedded therein; and a registration plate havingthe second set of markers embedded therein, the orientation andregistration plates being spaced from and parallel to each other.
 9. Theregistration fixture of claim 8, wherein the spacing between theorientation plate and the registration plate ranges between 25 mm and 50mm.
 10. The registration fixture of claim 1, further comprising a sideframe having a plurality of optical tracking markers and adapted todetachably mount to the base frame.
 11. A registration fixture for usewith a surgical navigation system for registration of medical images toa three-dimensional tracking space comprising: a base frame adapted tobe mounted to an x-ray medical imaging device; an orientation plateattached to the base frame and having a first set of non-uniformlyarranged radiopaque markers lying on a first circle; a registrationplate attached to the base frame and having a second set of uniformlyarranged radiopaque markers lying on a second circle larger than thefirst circle, the second circle being to the first circle and theorientation plate and registration plates being spaced from each other;and a side frame having a plurality of optical tracking markers andadapted to detachably mount to the base frame without piercing asterilizing drape to be interposed between the base frame and the sideframe.
 12. The registration fixture of claim 11, wherein the first setof markers include a plurality of subsets of markers with each subset ofmarkers and a corresponding marker in the first circle lying on animaginary line from the center of the first circle.
 13. The registrationfixture of claim 12, wherein each subset of markers includes at leasttwo markers that extend radially outwardly from the second circle. 14.The registration fixture of claim 11, wherein the number of markers ofthe first set and the second set is the same.
 15. The registrationfixture of claim 14, wherein the number of markers of the first set andthe second set is each
 24. 16. The registration fixture of claim 15,wherein all of the markers in the second set lie on the second circle.17. The registration fixture of claim 12, wherein all of the markers inthe second set lie on the second circle;
 18. The registration fixture ofclaim 11, wherein the orientation plate and the registration plate areparallel to each other.
 19. The registration fixture of claim 18,wherein the spacing between the orientation plate and the registrationplate ranges between 25 mm and 50 mm.
 20. The registration fixture ofclaim 11, wherein the side frame comprises: a first side frame extendinglaterally on one side of the base frame and having spaced apart opticaltracking markers facing away from the base frame in a first direction; asecond side frame extending laterally on the other side of the baseframe and having spaced apart optical tracking markers facing away fromthe base frame in a second direction opposite the first direction.